Spark plug

ABSTRACT

The disclosure relates to an improved spark plug assembly, including an improved low inductance spring. The spring is positioned within the bore of a spark plug, either in conjunction with a noise suppression resistor or otherwise. The spring is formed from an elongated resilient conductor which is preferably flat. The spring is shaped into generally an &#39;&#39;&#39;&#39;S&#39;&#39;&#39;&#39; configuration with a curl at each end.

United States Patent 1 91 Podiak 1451 Aug. 27, 1974 SPARK PLUG [75] Inventor: Richard S. Podiak, Maumee, Ohio [73] Assignee: Champion Spark Plug Company,

Toledo, Ohio 22 Filed: May 4,1973

1211 Appl. No.: 357,324

[52] US. Cl 313/118, 313/125, 313/136, 313/134 [51] Int. Cl. HOlt 13/04 [58] Field of Search 313/118, 134, 135, 136, 313/137,144,125,126

[56] References Cited UNITED STATES PATENTS 2,349,432 5/1944 Hopps 313/136 x 2,597,978 5/1952 Doran 313/136 X 2,635,598 4/1953 Field 313/135 x 3,603,835 9/1971 Eaton 313/135 x FOREIGN PATENTS OR APPLICATIONS 479,872 1/1952 Canada 313/136 Primary ExaminerAlfred L. Brody Attorney, Agent, or Firm0wen & Owen [57] ABSTRACT The disclosure relates to an improved spark plug assembly, including an improved low inductance spring. The spring is positioned within the boreof a spark plug, either in conjunction with a noise suppression resistor or otherwise. The spring is formed from an elongated resilient conductor which is preferably flat. The spring is shaped into generally an S configuration with a curl at each end.

7 Claims, 8 Drawing Figures SPARK PLUG BACKGROUND OF THE INVENTION This invention relates to ignition systems for internal combustion engines and more particularly to an improved spark plug having a low inductance spring for maintaining positive electrical contact between the upper center electrode and either the terminal stud of a spark plug or a noise suppression resistor in a spark plug, if one is used.

The use of a spring in the bore of a spark plug is known in the art. Springs compensate for the tolerances of the assembled parts and assure good electrical contact under all operating conditions. Often a spring is used in conjunction with a noise suppression resistor in the spark plug bore. Some prior art springs have been of the spiral coil variety, such as shown in U.S. Pat. No. 2,129,961. Sometimes coil springs serve as inductors that form resonant circuits with the capacitance inherent in the ignition system. When excited by spark discharges, these circuits will oscillate and radiate strong radio frequency signals. The values of capacitance and inductance are commonly such that the radiated signals will have a frequency falling within that portion of the frequency spectrum used for radio communication and other related services, thus causing undesirable interference.

U.S. Pat. No. 3,603,835 disclosed an improved pleated spring for spark plugs with suppression resistors. Another type in spring construction is shown in U.S. Pat. No. 2,635,598.

SUMMARY OF THE INVENTION According to the instant invention, an improved spark plug having a novel spring is provided for use in securing good electrical contact among the components in the bore of a spark plug or in some other suitable location in an ignition system. The spring is capable of performing its resilient mechanical and electrical mounting functions while having a minimum inductance, thus reducing the likelihood that undesirable radio interference will be created. The particular configuration of the spring makes it capable of great longitudinal adjustment with very little variation in load, which was a problem with many coil springs. Thus a spring of given length is quite versatile in being applicable to many different spark plug embodiments with different size spacings for a spring. The spring is formed into generally an S-shape from an elongated piece of resilient conductive material which preferably has a rectangular or flat cross section. At each end of the elongated piece of material is a curl. The two curls extend in opposite directions laterally to the elongated portion of the spring. On compression of the spring the curls roll up further, giving the spring its quality of Iongitudinal versatility.

Accordingly, it is a primary object of the invention to provide an improved spark plug having a lowinductance spring for maintaining good electrical contact among the components in the bore of a spark plug.

Another object of the invention is to provide a spark plug wherein the spring is capable of relatively large longitudinal adjustment with very little corresponding variation in load.

Other objects and advantages of the invention will become apparent from the following detailed description, reference being made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional elevational view of a spark plug assembly according to the instant invention;

FIG. 2 is a sectional elevational view of another embodiment of a spark plug assembly, including a noise suppression resistor according to the instant invention;

FIG. 3 is an enlarged cross-sectional view taken along the line 33 of FIG. 1;

FIG. 4 is a side view of the spring;

FIG. 5 is a perspective view of the spring;

FIG. 6 is a diagrammatic elevational view of a partially compressed spring;

FIG. 7 is an elevational view of another embodiment of the spring; and

FIG. 8 is a diagrammatic elevational view of a further embodiment of the spring shown partially compressed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a spark plug, according to the instant invention, is indicated by the reference number 10. The spark plug 10 includes a spring 11, an outer shell 12 having a threaded lower end 13 for engaging the head of an internal combustion engine and an insulator 14. The insulator 14, which is mounted within the shell 12, has an axial bore 15 for mounting a center electrode 16. The center electrode 16 has a firing tip 17 which defines a spark gap with a ground electrode 18, which is attached to the threaded end 13 of the shell 12. The center electrode 16 is electrically connected in series through the spring 11 to an external terminal 19. A good electrical contact will be maintained by the spring 11, even though the electrode 16 expands and contracts as the spark plug 10 is heated and cooled.

Referring now to FIG. 2, another embodiment of a spark plug according to the present invention is generally indicated by the reference number 20. The spark plug 20 has an interference suppression resistor 21 and a short spring 22. The spark plug 20 also includes an external terminal 23 and a center electrode 24. The resistor 21 may, for example, be either conventional carbon resistor or a wire wound resistor. The spring 22 forces the resistor 21 against the external terminal 23 to maintain an electrical contact between the resistor 21 and the terminal 23 and to simultaneously maintain an electrical contact between the resistor 21 and the center electrode 24. A good electrical contact will be maintained by the spring 22 even though both the resistor 21 and the electrode 24 expand and contract as the spark plug 20 is heated and cooled. It will be appreciated that although the spring 22 is shown between the resistor 21 and the center electrode 24, the spring 11 may be similarly positioned between the resistor 21 and the external terminal 23.

Referring now to FIGS. 4-6, the spring 11 is shown in detail. Although the spring 11 may be formed from a resilient wire, it is preferably formed from an elongated resilient piece of conductive material having a generally flat or rectangular cross section, as shown.

The spring 11 has two opposed end portions A and B. As shown in FIGS. 5 and 6, end portions A and B are both formed into curls but extend in opposite directions from an elongated or extended central portion C. Each curl defines a turn of at least about 360 and terminates in a right angle bend. In the present embodiment, the bends define flat portions 25 and 26 which extend radially inward toward the center of the curls. As shown in FIG. 4, the side profile of the spring 11, when either compressed or uncompressed, is flat. The flat profile significantly reduces the inductance of the spring 11.

The spring 11 is shown in FIG. 6 compressed between the electrode 16 and the external terminal 19. End portions A and B are maintained in forced electrical contact with electrode 16 and external terminal 19. When the spring 11 is compressed, end portions A and B continue to curl. FIG. 6 shows additional curling of about one half turn. The load on spring 11 increases very little as it continues to curl and the overall vertical length of the spring 11 is shortened. Thus the spring 11 is versatile in application to various size spacings in dif-' ferent spark plugs, and in a given spark plug such as the spark plug shown in FIG. 1 the load variation during heating and cooling expansion and contraction is almost nil.

In FIG. 2 the spark plug includes a radio interfer ence suppression resistor 21, retained by a short spring 22. It will be appreciated that the structure and function of spring 22is identical to that of spring 11 of FIGS. 1, 3, 4, 5 and 6, except that spring 22 is shorter to accommodate resistor 21. Spring 22 secures and maintains good electrical contact from external terminal 23 through resistor 21 and spring 22 to electrode 24.

FIGS. 7 and 8 show two additional embodiments of a conductor spring for maintaining electrical contact in the bore of a spark plug, such as the spark plug 10 of FIG. 1. In FIG. 7 a spring 27 includes curled end portions D and E which extend in the same direction from a central extended portion F.

A spring 28 of FIG. 8 is diagrammatically shown compressed between the electrode 16 and the external terminal 19 of the spark plug 10 of FIG. 1. The spring 28 is similar to the spring 27 in that it has end portions G and H extending in the same direction. However, the spring 28 has a curved or bowed central portion I which extends in the same direction as the end portions G and H.

I claim:

1. A spark plug for an internal combustion engine having an insulator surrounding a center electrode, a terminal adjacent the upper end of said insulator, an elongated and freely movable conductor spring positioned within the bore of said insulator for maintaining electrical contact between said center electrode and said terminal, said spring formed from a flat elongated conductor and having a longitudinal centerline, two opposed end portions and a central portion, each of said end portions being formed into a spiral curl, the arcuate centerline of each of said spiral curls and the centerline of said central portion lying in a single plane, whereby said spring is free to expand and contract along such centerline as said spiral curls roll and unroll under axial compression during operation of the engine.

2. A spark plug according to claim 1 wherein said spiral curl comprises at least one 360 turn.

3. A spark plug according to claim 1 wherein said spiral curls extend outwardly from said central portion in opposite directions, generally defining an S-shape.

4. A spark plug according to claim 3 wherein said spiral curls are of substantially equal size.

5. A spark plug according to claim 1 wherein an interference suppression resistor is positioned in the bore of said insulator between said center electrode and said terminal, said spring being positioned adjacent said resistor.

6. A spark plug for an internal combustion engine having an insulator surrounding a center electrode, a terminal adjacent the upper end of said insulator, an elongated and freely movable conductor spring positioned within the bore of said insulator for maintaining electrical contact between said center electrode and said terminal, said spring formed from a flat elongated conductor having a longitudinal centerline, two opposed end portions and a central portion, each of said end portions being formed into a spiral curl, said spiral curls extending outwardly from said central portion in opposite directions and being substantially of an equal size, the arcuate centerline of each of said spiral curls and the centerline of said central portion lying in a single plane, whereby said spring is free to move along such centerline as said spiral curls roll and unroll during operation of the engine.

7. A spark plug according to claim 6 wherein each of said spiral curls comprises at least one 360 turn. 

1. A spark plug for an internal combustion engine having an insulator surrounding a center electrode, a terminal adjacent the upper end of said insulator, an elongated and freely movable conductor spring positioned within the bore of said insulator for maintaining electrical contact between said center electrode and said terminal, said spring formed from a flat elongated conductor and having a longitudinal centerline, two opposed end portions and a central portion, each of said end portions being formed into a spiral curl, the arcuate centerline of each of said spiral curls and the centerline of said central portion lying in a single plane, whereby said spring is free to expand and contract along such centerline as said spiral curls roll and unroll under axial compression during operation of the engine.
 2. A spark plug according to claim 1 wherein said spiral curl comprises at least one 360* turn.
 3. A spark plug according to claim 1 wherein said spiral curls extend outwardly from said central portion in opposite directions, generally defining an S-shape.
 4. A spark plug according to claim 3 wherein said spiral curls are of substantially equal size.
 5. A spark plug according to claim 1 wherein an interference suppression resistor is positioned in the bore of said insulator between said center electrode and said terminal, said spring being positioned adjacent said resistor.
 6. A spark plug for an internal combustion engine having an insulator surrounding a center electrode, a terminal adjacent the upper end of said insulator, an elongated and freely movable conductor spring positioned within the bore of said insulator for maintaining electrical contact between said center electrode and said terminal, said spring formed from a flat elongated conductor having a longitudinal centerline, two opposed end portions and a central portion, each of said end portions being formed into a spiral curl, said spiral curls extending outwardly from said central portion in opposite directions and being substantially of an equal size, the arcuate centerline of each of said spiral curls and the centerline of said central portion lying in a single plane, whereby said spring is free to move along such centerline as said spiral curls roll and unroll during operatIon of the engine.
 7. A spark plug according to claim 6 wherein each of said spiral curls comprises at least one 360* turn. 